Method of cold pressure welding metal foil



July 14, 1959 v. CLAIR, JR 2,894,322

METHOD OF cow PRESSURE WELDING METAL FOIL 'Original Filed July 12, 1954i. giwmfi f WV a m /6 ,7 INVENTOR Vim E C24? a7.

BY fig/qaa ATTORNEY 1 METHOD OF COLD PRESSURE WELDING METAL FOIL VerneClair, In, Levittown, N.Y., assignor, by mesne asdisclosed by theabove-mentioned patent, a practical limit is soon reached for members ofgreatly reduced thicksignments, to Kelsey-Hayes Company, 'Detroit, Micha corporation of Delaware Original application July 12, 1954, Serial No.442,558, now Patent No. 2,763,057, dated September 18, 1956. Divided andthis application August 15, 1956, Serial No. 604,168

2 Claims. (Cl. 29-4701 ness, practically from about 0.030" on downward,and better known as sheets or foils, where any efiective and reliablewelding will no longer be possible, both on account of the minute sizeof the welding tools or areas and due to the increased difficulty ofcontrolling the tool penetration or indentation required to insurepositive and dependable welding.

It has already been proposed, as described in U.S. Patent No. 2,707,889,to weld relatively thin members of pressure weldable material, such asmetal sheet or foil, by the use of a modified and improved technique andmethod comprising applying welding pressure to a striplike area of thelapped sheets whose widthis a substantial multiple of, that is at leasttwice, the gauge thickness of the members being welded. As a result ofthe increased width of the weld area or pressure tool face, metal is notonly caused to flow laterally and in the direction of the interfacebetween the members, as in the case of welding relatively thickermembers by using a tool width of the order of the gauge thickness of the.In the art of cold pressure welding of metals or welding underconditions where no liquid phase is produced or introduced into the weldat any stage, that is, where Welding is effected solely by pressure andwithout the application of extraneous welding heat, a suitable design ofthe pressure welding tools and a proper control of the members, butthere is produced a stretching or drawing action on the metal, causingan expansion or metal flow around the Welding tool or tools andresulting in a distortion of the members in a direction at right angleto the plane thereof. This stretching action or coexpansion of thecontacting metal surfaces, while promoting the formation of an efiicientweld has the further elfect of breaking up or dispersing the superficialoxide film usually present upon the surface, especially in the case toolpressure, after properly cleaning the areas of con- A tact to be joined,results in an interfacial cold or plastic flow of the metals of theadjoining surfaces conducive to effect merging into a solidphase'w'elding bond or joint.

There has already been proposed, as described for expable of coldpressure welding. More specifically, said patent discloses varioustechniques and tools for producing either a continuous line weld or'aspot weld at one or more limited areas of a pair of members to bewelded.

Since, as described in said patent, in cold pressure welding metal mustflowlaterally of the areas subjected topressure by the welding tools,or, in other words since themetal of the contacting surfaces is expandedunder pressure such as to effect merging into a true solid phase weldingbond, the mostefiicient tool shape or pressure area for the welding ofmembers. of relative large gauge thicknesses has been found to be of astrip-like or rectangular shape or area, the width of the strip orrectangle being, approximately equal to or of the order of the gaugethickness of the members being welded, but not being any more thanabouttwice said thickness.

The shape or width of the weld area, in addition-to involving a minimumof distortion and tool penetration, that is, about 60% of the totalthickness of the members for aluminum and about 86% for copper, insuresa favorable and unimpeded flow of metal laterally of the contactingsurfaces,whereby to enable the attainment of an intimate; and reliableweldedbond of adequate mechanical strength and other desirablecharacteristics.

In effecting laplpr es sure weld according to this technique, asthethickness of-the members tobe welded decreases, thenecessarilyreduceddimensionl of the pressure tools makes it increasingly difiicultto control the tool pgnetrationso asto prevent'damage'tothe membersandto. insure eificient and consistent welding with suffi ient re ent-9v Asa result, in, following 'the technique of aluminum, into smallparticles, whereby, in most cases, to enable welding withoutpre-cleaning of the members, except for the removal of contaminatingforeign matter, such as dirt, grease, etc. As a result, thecross-section of the resultant weld joint assumes the shape of a troughor channel due to the drawing effect or upfiow of the metal around theedges of the welding tool or tools.

It has been found, in cold pressure welding, that the most criticalphase during the welding operation is the starting of the welding actionor mutual pickup ofthe metals of the two members while, withweldinghaving oncebeen initated at a limited area, usually in the center of theweld line or strip, it will spread readily to the edges or periphery ofthe Weld area during continued pressure application. In making a foilweld of the type described, an initial and safe pickup of the metals'isinsured by the drawing or stretching action on the metals, thus insuringmerging and welding positively and reliably.

While it has thus been possible to produce an efiicient and reliablecold weld joint between two relatively thin members, such as sheets orfoils, it will be understood that such a weld or joint still suffersgreatlyfrom a strength point of view, whereby to render its use limitedif not prohibitive for many practical purposes and applications. Boththe substantial metal reduction at the weld area as well as the linearshape of the weld, result in a low resistance to bending of the joint aswell as other defects well known and understood. Accordingly, animportant object of the present invention is the provision of animproved method of cold pressure welding a pair of metal members ofrelatively. small thickness, such as sheets or foils, whereby the aboveand related defects and drawbacks are substantially eliminated.

Another object of the invention is the provision of a combined coldpressure welding and/or pressing method for joining together two metalfoil members or the like, whereby to attain both an efficient weld jointbetween the members and to improve the mechanical strength ofthe jointproduced by a single operating step or pressure application.

In order to attain the above objects and purposes, there is described inthe above-named parent application, Serial No. 442,558, an improvedmethod of welding relatively thin rnenrbers such as metal foil, that isfor all practical purposes, members having a thickness of less thanabout 0.930 inch which method comprises essentially the steps ofsuperimposing a pair of foils or sheets with the portions thereof to bejoined in contacting relation, applying indenting pressure to .aplurality of substantially identical and evenly distributed weldingareas, said areas having a width in any direction equal to a multiple ofand at least twice the foil thickness, whereby to reduce the metalthickness and to create a drawing action at said areas out of theinitial plane of the sheets etc. as well as to cause a metaldisplacement laterally of said areas. Furthermore, the spacing distancesbetween the welding areas are so related to the foil thickness as tocausethe metal displaced from each indented area to oppose the metalflow from. an adjacent area, whereby to force the displaced metals ofthe intervening nonindented areas out of the plane of the foils or thelike members, in such a manner as to produce a uniformly distorted orcrinkled shape of the portions upon welding thus to strengthen the jointobtained mechanically.

' In a method of this character, the indented or weld areas are in theform of parallel lines spaced at proper distances from one another,whereby to result in a cor rugated and mechanically strengthened joint.The bend ing. of such a joint is, however, limited to bending about anaxis at right angle to the weld lines or corrugations, .while'littlestrength exists against bending about a line parallel to saidcorrugations. For a joint to have an equal strength in more than onedirection, the indented or weld areas should be in the form of weldspots, such as of square, rectangular or other suitable shape, saidspots being evenly distributed over the entire joint at a proper mutualspacing from one another in the manner ofa mosaic or uniform pattern.

As described in said copending parent application, for producing a weldof this type, the tools used may comprise a first tool member having aflat surface to serve as an anvil and a'second cooperating tool memberalso provided with a fiat surface and having projecting therefrom aplurality of indenters conforming with the desired multiple weld areas,that is, either in the form of parallel ribs or tongues or a pluralityof uniformly distributed and equallyspaced welding tips, respectively.

While in the case of parallel weld lines and a resultant corrugatedjoint, the tools or dies may be simply and accurately produced by theprovision of parallel grooves or flutes machined in the tool surface,considerable difiiculties are encountered in producing a large number ofrelatively small welding tips, especially in the case of sheets of foilof reduced thickness, such as to afford efiicient and safe welding atall the weld spots or points and'to prevent damage to the foils andother drawbacks, as will be readily understood.

Accordingly, another object of the invention is the provision of asimple'and eificient method of making a multiple spot weld joint of twometal foil pieces or the like, while at the same time mechanicallystrengthening the joint produced.

The above and further objects, as well as novel aspects of theinvention, will be better understood from. the following detaileddescription taken in reference to the accompanying drawings forming partof. this specification and her V Fig. I shows on an exaggerated scaleand iuschcmatic fashion a welding tool and a pair of metal foils. or thelikeinserted therein to be welded, the tool and foils being shown in theposition prior to welding;

"Fig. is a top View, on a reduced scale, of one ofthe tool members takenon line 22- of Fig. 1;

Fig. 3 shows the tool of Fig. land foil; in the position after welding;and

Fig. 4 is a top view showing a pair of foil pieces welded by means ofthe method according to the invention.

Like reference characters identify like parts in the different views ofthe drawing.

With the foregoing and further objects of the inven* tion in view, aswill appear hereafter, the above mentioned and related difficulties aresubstantially overcome by an improved method and technique of weldingmetal foils or the like members involving generally the production of a.multiplicity of uniformly spaced weld spots or areas and an automaticcontrol of the welding operation, on the one hand, and a strengtheningof the welded joint by a crinkling, 'knotting or the like effect of thewelded metals.

This combined eifect of welding and strengthening of the joint obtainedis achieved by the use of a pair of welding tool members having flatsurfaces and projecting therefrom a plurality of parallel indenting ribsor tongues of suitable width and relative spacing. The tools arearranged with the ribs of one tool member crossing or intersecting theribs of the other tool member, whereby, in addition to the indenting andwelding of the members at the crossover or intersecting points of thewelding ribs, to effect both a control of the welding operation and astrengthening or stiffening of the welded joint obtained. In otherwords, while using simple linear indenters or welding ribs which can beproduced to exacting specifications, the resultant joint is of the typecomprising a mosaic like pattern of a great number of uniformlydistributed and relatively evenly spaced weld spots or areas, providingadequate 'mechanical strength to bending in substantially alldirections.

In other words, the present invention is predicated on the thought ofutilizing the stretching effect or upflow of the displaced metal in afoil weld process using tools suitably related to the foil thickness, todeform or cause a buckling effect on the metal between the indentedareas, thus strengthening the joint obtained against bending insubstantially any direction.

Referring more particularly to Figs. 1 and 2 of the drawing, there isshown a tool arrangement according to the invention for welding tworelatively thin members 10 and 11, such as metal sheets or foils, etc.,said tool comprising essentially a lower tool member 12 having a flatsurface and projecting therefrom a plurality of tapering and parallelindenters or welding ribs 15' of a width w and being spaced from oneanother by predetermined distances d. More particularly, the width w ofthe indenters is a multiple of, that is at least twice the gaugethickness t'of the members 10 and 11, while the distance d between theadjacent indenters, for most practical purposes, should be greater thanor about 1.5 times the width w, as shown in the example of the drawing.The dimensions w and d may be advantageously determined by experiment,it being essential only, that the width of the indenters is a sufficientmultiple of the gauge thickness t, to cause the necessary upflowof themetal around the tool members 12 and 13 and to effect a buckling of theintervening non-indented areas, as described in the following and shownin Fig. 3.

Furthermore, the height h of the indenters, while not critical, shouldbe such as to afford a ready displacement and buckling of the metal, toinsure adequate metal flow at the indented areas conducive to welding,on the one hand, and to enable the displaced metal to move at a rightangle to themembers and to produce a strengthening of the jointobtained; The tapering angle a of the indenters maybe about 15, althoughthis value is not critical andmaybe varied within limits. The tools 12and 13 may be constructed from mild steel or from unha-rdened chromemanganese tool steel, the latter being especially suitable forthe-welding of aluminum sheet or foil.

Thecooperating or upper tool 13 also has a flat surface andprojecting-therefrom a plurality of parallel welding rib??? strip likeindenters 14- or supporting surfaces, re-

spectively, arranged] at an angle, such as a rightangle, to theindenters15 of the tool member. 12', whereby to cross the latter at a pluralityof intersection points constituting the actual indenting or weld areas.Preferably theindenters 14 and 15 form an. angle 5, Fig. 2, with theshort axis of the tool face, such as about 30 as shown in the drawing,to result in maximum mechanical strength and stiffness as will becomefurther apparent from the following.

In a tool of the type described, themetal at the contacting orintersecting areas of the indenters 14 and 15, upon: the applicationofsuitable welding pressure to the tool rnembers in the directionindicated by the arrows a in the drawing by means of a hand press or thelike, is subjected to adrawing.action,ficausing an expansion orstretching of the metals atthe interface and resulting in a safeinitiation of the welding or merging of the interfacial surfaces into anintimate union or solid phase welding bond. At the same time, thestretching effect causes a breaking up or dispersion of the superficialoxide film usually present upon the surface of the members, especiallyin the case of aluminum, whereby to allow welding without precleaning,at least as far as removal of the oxide film is concerned.

Furthermore, due to the specific relationship between the width w of theindenters 14 and 15, the gauge thickness 1 and the spacing distances d,the metal at the areas d is allowed to move freely so as to flow outsideof the indented areas in a direction substantially at right angle to theinterface, that is, in other words, to cause an upflow or buckling ofthe members, as shown at p in Fig. 3. In other words, the metal betweenthe welded areas is formed into a plurality of protuberances or knots16, Fig. 4, resulting in mechanical strengthening or stiffening of thewelded joint.

In addition to the combined welding and crinkling of the members as aresult of the single pressure operation, the invention has the furtheradvantage of automatically controlling the welding or tool penetrationto result in efiicient and consistent joints, without requiringauxiliary control or stop means for the tool members 12 and 13.

More specifically, provided a proper design of the width w of theindenters 14 and 15, as well as the spacing distance d and the height hof the indenters, the metal is allowed to flow relatively unimpededduring the initial stage of the pressure application, thus causingindentation and welding, in the manner described. As the pressureapplication is continued the flow of the metal displaced laterally ofthe weld areas at the intersection points of the indenters will beincreasingly opposed by the metal displaced in the opposite directionfrom an adjacent weld point or area, whereby to result both in astiffening or crinkling of the members, on the one hand, and toautomatically control the indentation or metal reduction required toproduce an adequate metal flow conducive to welding at the intersectionspots or areas. As a result, by the proper tool design, welding may becontrolled accurately and consistently in a most simple manner, comparedwith other cold pressure welding methods which require special stop andauxiliary means to control and limit the depth of indentation for safeand reliable welding. This advantage of the invention is of specialimportance in the welding of thin sheets or foils, where slightdiscrepancies in the tools or control may result in cutting or otherdamage to the members, in view of the minute size and dimensions as wellas tool penetration involved.

In practice it has been found that welding may be effected over aconsiderable range of gauge thicknesses and with materials of any givenductility or degree of cold weldability, provided the width of theindenters is a suitable multiple of the gauge thickness and that thespacing distances or gaps between adjacent indenters are so designed asto enable ready lateral metal flow to enable welding, on the one hand,and to strengthen the '6 resultant joint in the manner described, on theother hand. I M

It has furthermore been found that pressure welding of two members at anarea or spot having substantially equal dimensions in all directions,such as a circular, square or the like area, is difficult withouteifecting ex cessive metal reductionor without limiting the joint to theedge portion or periphery of the area, due to the limited and uniformmetal flow in substantially all directions, wherefore the advantage of arectangular or striplike weld area causing a preferential flow at rightangles tothe larger side of the rectangle or weld strip. By the presentinvention, this difiiculty is principally overcome by the use ofstrip-like indenters insuring adequate flow of the metal during welding,while limiting the weld joint to a plurality of uniformly spaced weldspots at the areas of intersection of said indenters. In other words,the invention by using known and proven techniques in,a new combinationachieves both a strong and reliable multiple spot weld at areas havingsubstantially equal dimensions in all directions, substantially withoutthe drawbacks and defects inherent in the previous prior art methods.

This is shown more clearly in Fig. 4, wherein the numerals 18 indicatethe channels produced by the indenters or ribs 14 and 15 by thestretching and upflow of the metal around the edges of the indenters asa result of the width w being a multiple of the gauge thickness 1 of themembers 10 and 11. The same channels 18 appear upon the underside of themembers 10 and 11. This stretching effect or metal flow laterally of thechannels or strip-like areas 18 results in a welding at the intersectingspots or areas 17 of the ribs 14 and 15 due to the increased pressurethereat at right angle to the interface. At the same time, the metaldisplaced laterally of the areas 18 is distorted or forced in adirection transverse to or out of the planes of the foils or members 10and 11, in such a manner as to result in a uniform embossing orcrinkling of the entire welded area as shown at 16, causing a stiffeningor increased mechanical strength of the total welded area againstbending in substantially all directions.

Accordingto a practical example, a tool having indenters of a width wequal to 0.020, a spacing distance d equal to 0.035" and a height hequal to 0.030, has been found suitable for satisfactorily weldingaluminum foils within a thickness range from about 0.002 to 0.010". Forother thicknesses and materials of different ductility the mostfavorable tool dimensions can be determined simply by experiment byfollowing the basic considerations and requirements as pointed outhereinabove.

In the foregoing the invention has been described with reference to aspecific illustrative device and method. It will be evident, however,that modifications and variations, as well as the substitution ofequivalent elements and steps for those shown and described forillustration, may be made without departing from the broader scope andspirit of the invention as set forth in the appended claims. Thespecification and drawings are accordingly to be regarded in anillustrative rather than in a limiting sense.

I claim:

1. A method of welding relatively thin members of ductile cold pressureweldable metal having a thickness of less than about 0.030 inchcomprising superimposing said members with the portions to be joined incontacting relation, supporting one side of the superposed members by aplurality of spaced, parallel and strip-like supporting surfaces havinga width equal to a multiple of the gauge thickness of said members,applying a pressure to the opposite side of the superposed members overa plurality of spaced, parallel and strip-like pressure areas having awidth substantially equal to the width of said supporting surfaces, saidsupporting surfaces intersecting said pressure areas at a predeterminedangle to each other, and continuing the pressure application to cause astretching of the metals laterally of and an upfl'ow around the edges'ofsaid areas, thereby to result in an intensified 'interfacial actionby the added pressure at the intersecting portions of said areasconducive to producing a plurality of solid phase spot-like Weldingjoints thereat, While distorting the areas exterior of said joints outof the planes of said members, to result in a mechanical strengtheningof the total Welded area of said members.

'2. A method of welding relatively thin ductile metal members having athickness'o-f less than about 0.030 inch comprising superimposing saidmembers With the areas to be joined in contacting relation, supportingone side of the superposed members by 'a plurality of parallel andstrip-like supporting surfaces having a Width equal to a multiple of thegauge thickness of said members and spaced by distances equal to about1.5 times said width, applying a pressure to the oppositejside of themembers over a plurality of spaced, parallel and strip-like pres- 8 sureareas having a width and relative spacing substantially equal to thewidth and relative spacing of said supporting areas, said supportingarea's intersecting said pressure areas "at a' predetermined angle toeach other, and continuing the pressure application to cause astretching of the metals laterally of and an u flew around tl'r' e edgesof said areas, thereby to' result in an intensified interfacial actionby the added pressure at the intersect ing portions of said areasconducive to roducing a plurality of spot-like solid phase Weldingjoints' thereat, while distorting the areas exterior of said joints"outot the planes of said members; to result in a "mechanicalstrengthening of the total Welded area of said members;

References Cited in the file of this patent F UNITED STATES PATENTS1,253,189 Von I-Ienke Ian. s, 1918' 2,522,408 Sowter Sept. 12, 19502,763,057 Clair -Sept. 18, I956

